i) Field of the Invention
This invention relates to processes for producing diarylacetylenes and enamines which are valuable in the synthesis of homopolymers and copolymers, for example, poly(arylether)s, polyesters, polycarbonates and polyformals.
ii) Brief Description of Prior Art
Advanced composite materials are made from combinations of high performance fibers, such as glass, graphite, carbon, silicon carbide or ceramic fibers, arranged in close packed alignment in the polymer as a matrix. Such composite materials provide a combination of strength and modulus superior to that of structural metals and alloys on an equal weight basis. Such composites are, for example, employed in military and commercial aircraft, and space vehicles, as well as in sports and sailboats.
These composite materials are expensive, and so their use is confined to relatively high cost items. On the other hand, even though the raw materials for these advanced composites are expensive, over 70% of the costs associated with such composites result from the processing costs for their manufacture.
In particular, the currently used manufacturing processes produce volatiles during curing of the polymer matrix and such volatiles produce voids in the matrix which act as sites for structural failure. In order to minimize void formation during evolution of volatiles, the cure must be carried out over a long period, under reduced pressure and this manufacturing requirement is a major factor in the production cost.
Acetylenic groups have been proposed in polymers in order to provide reactive sites for cross-linking the polymers when heated. The potential advantage of such acetylenic groups is that no volatiles will be produced during curing or cross-linking.
The acetylenic groups have been introduced into polymer chains as terminal groups, pendant groups or internal groups.
Acetylene precursor polymers have been reviewed by Hergenrother (P. M. Hergenrother, J. Marcromol. Sci.-Rev. Macromol. Chem. C19(1), 1-34 (1980).
Most of the polymers with terminal acetylenic groups, that have been synthesized contain unsubstituted ethynyl groups on the ends of the polymer chains and they are generally end-capped low molecular weight oligomers which are synthesized in order to provide easier processability. Reinhardt et al (B. A. Reinhardt, F. E. Arnold and M. R. Unroe, U.S. Pat. No. 4,513,131 (1985)) have synthesized the simple bis(phenylethynylphenyl)ethers as potentially thermally curable resins and studied their thermal curing properties.
Polymers containing pendant phenylethynyl groups have been synthesized and these polymers have been thermally cured. Examples are described in the afore-mentioned Hergenrother article and in U.S. Pat. No. 4,375,536 (1983) of Hergenrother.
Polymers containing internal acetylene groups have been less studied. T. Takeichi, H. Date and Y. Takayama, J. Pol. Sci. Chem. Ed. 28, 1989 (1990) describes the synthesis of polyimides containing internal acetylene groups. The authors indicate that the diphenylacetylene groups must be linked in the metal position to provide effective cross-linking.